Air-cooled heat exchanger with reduced noise level

ABSTRACT

An air-cooled heat exchanger can be operated at lower noise levels by providing fans both above and below the tube bundle. Operation at lower fan speed can be achieved, with maintenance of the necessary air displacement for cooling, and reduction in overall noise level.

[111 3,840,067 1451 Oct. 8, 1974 AIR-COOLEI) HEAT EXCHANGER WITH REDUCED NOISE LEVEL [75] Inventor: Willem Herman Bos, Rijswijk,

Netherlands [73] Assignee: The Lummus Company, Bloomfield,

221 Filed: May 2,1973 21 Appl. No.: 356,306

[30] Foreign Application Priority Data 12/1970 Gunter 165/111 4/1973 VonCleve 165/125 FOREIGN PATENTS OR APPLICATIONS 904,959 9/1962 Great Britain 165/122 705,834 5/1941 Germany 165/122 Primary ExaminerCharles J. Myhre Assistant Examiner-Theophil W. Streule, Jr. Attorney, Agent, or Firm-Richard J. Holton An air-cooled heat exchanger can be operated at lower noise levels by providing fans bothabove and below the tube bundle. Operation at lower fan speed can be achieved, with maintenance of the necessary air displacement for cooling, and reduction in overall May 4, 1972 Netherlands 7206046 [57] ABSTRACT 52 us. ca. 165/1, 165/122- [51] Int. Cl F28f 27/00 [58] Field of Search 165/111, 122, 1, 2; 261/111; 415/179 [56] References Cited noise leveL UNITED STATES PATENTS 1 Claim, 1 Drawing Figure 3,048,006 8/1962 Goodman 415/179 PATENIHJ BET 8 974 v LFLI AIR-COOLED HEAT EXCHANGER WITH REDUCED NOISE LEVEL BACKGROUND AND PRIOR ART The invention relates to an air-cooled heat exchanger comprising of plurality of tubes, wherein a fluid (i.e. liquid or gas) to be cooled or condensed flows through the tubes, and wherein an air current derives from the output of an axial ventilator, i.e., fan, flows around the tubes, the main direction of the air current being substantially perpendicular to the longitudinal direction of the tubes. Depending on various design factors, the exchanger may be of the forced draft type, in which the axial ventilator is located below the tubes, and forces air up around them, or of the induced draft type, in which the axial ventilator is located above the tubes and draws air up through them.

In air-cooled heat exchangers of this type, of the usual sizes and cooling capacities, the speed of rotation of the blade wheel of the axial ventilator is often so high that an annoying sound is generated due to air turbulence at the outer ends of the blades. With increasing concern over noise pollution and increasing size of industrial air-cooled heat exchanger installations, noise abatement has become an important factor in the design of such equipment. It is an object of the invention to provide an air-cooled heat exchanger, especially one for large scale industrial use, which can be operated at lower noise levels.

SUMMARY OF THE INVENTION According to the invention a second axial ventilator or fan is provided on the side of the tubes remote from the first mentioned axial ventilator in such manner that the input of the second ventilator faces the tubes. Since in the air-cooled heat exchanger according to the invention the air displacement isno longer effected by a single axial ventilator, but by two axial ventilators, it is possible to operate the fans of the ventilators at a considerably lower speed of rotation while maintaining the same cooling capacity, whereby the sound generated is substantially decreased and reduced to such a level that it is no longer annoying.

DETAILED DESCRIPTION OF THE DRAWING AND PREFERRED EMBODIMENTS The invention may be further elucidated by reference to the drawing, in which one embodiment of an aircooled heat exchanger according to the invention is schematically shown in a vertical cross section. The drawing, however, is not intended to limit the invention as various modifications apparent to those skilled in the art may be utilized.

The exchanger comprises a frame 1 supporting one or more bundles of tubes (shown schematically) comprising a plurality of horizontal tubes 3, preferably provided with external fins 2 and connected at one end with a supply of the fluid to be cooled or condensed and at the other end with a discharge for the cooled or condensed fluid.

Frame 1 is supported by underlining structure 4 closed at the sides and is self-supported by legs 5. A on cular opening in the bottom 4'of the supporting structure 4 contains an air guiding ring 6 spacedly surrounding the blade wheel of a first axial ventilator or fan 7.

Frame 1 is connected by means of a conical wall 8 with a cylindrical outlet ring 9 spacedly enclosing the blade wheel of a second axial ventilator or fan 10.

The vertical shafts l1, 12 of the blade wheels of fans 7, 10 are interconnected by the means of an intermediate shaft 13, the ends of which are connected with the shafts 11 and 12 by means of flexible couplings 14, 15; the intermediate shaft 13 is enclosed by a sleeve 16 extending through the tube bundle. l

A further advantage is achieved when the tubes are provided with fins 2 which, in addition to aiding in cooling the fluid passing through the tubes, also serve as a guiding for the air passing over the tubes. The air thereby becomes conditioned for the fan or ventilator located in the second, or upstream position in relation to the direction of the air flow. Thus the tubes of this exchanger can serve as a dual function.

A drive motor 17 drives the shaft 11 of the axial ventilator 7 by means of a gear 18, whereby the shaft 12 of the axial ventilator 10 is also driven to the intermediate shaft 13. The axial ventilator 7 and 10 may be provided with blade wheels having adjustable blades and may be selected in such manner that they may effect together the air displacement required for the desired cooling capacity at a rotational speed of the blade wheels such that no annoying sound is generated. In operation, air from the surrounding atmosphere is drawn in by the lower axial ventilator 7; the air flows in an upward direction through the space enclosed by the supporting structure 4 and along tubes 3 of the bundle, after which is drawn out by the upper ventilator 10. The tubes 3 operated as a guiding system conditioning the flowing air for the upper axial ventilator 10.

The drawing depicts the two ventilators 7 and 10 as being driven by a common drive motor 17; however, it is equally possible to utilize a separate motor to drive each ventilator.

To evaluate the invention, an existing air-cooled heat exchanger was equipped with a second axial ventilator. Both fans had six blades and a diameter of 14 feet. Before installation of the second fan, the single fan was operated so as to displace about 200,000 cubic feet per minute of air. This required operation of the fan at 160 rpm and total pressure of 0.52 in. water gauge, and resulted in a power (noise) level of 90.5 dB(A), which was quite annoying. With the second fan installed and in operation, a displacement of about 195,000 cubic feet per minute of air could be maintained, as total pressure of 0.51 in. water gauge, with both fans operating at only rpm. The noise level was reduced to a more bearable level of about 86 dB(A) (dB RE l0 watts).

I claim:

1. A method of operation of an air-cooled heat exchanger having a plurality of substantially horizontally disposed tubes, wherein a fluid to be cooled or condensed flows through the tubes, and wherein an air current is caused to flow substantially perpendicularly to the longitudinal direction of the tubes, by a first fan means, comprising providing a second fan means on the side of the tubes remote from the first fan means in such manner that the air input of the second fan means faces the tubes, and reducing the rotational speed of the first and second fan means while maintaining substantially the same rate of flow of air over the tubes, whereby the total noise level of the fan means becomes reduced. 

1. A method of operation of an air-cooled heat exchanger having a plurality of substantially horizontally disposed tubes, wherein a fluid to be cooled or condensed flows through the tubes, and wherein an air current is caused to flow substantially perpendicularly to the longitudinal direction of the tubes, by a first fan means, comprising providing a second fan means on the side of the tubes remote from the first fan means in such manner that the air input of the second fan means faces the tubes, and reducing the rotational speed of the first and second fan means while maintaining substantially the same rate of flow of air over the tubes, whereby the total noise level of the fan means becomes reduced. 